Message text written by aribert
>My '71 GT6 has a Crane XR-700 ignition system. With the engine
running: alternator voltage is 14.2v, voltage into ballast resistor is
13.8v, voltage out of the resistor is 9.2v. Ballast resistor reads 1.7
ohm (catalog rated at 1.35 ohm). My coil (MSD Blaster 2) reads 1.1 ohm
across the terminals. NOTE: both of my multimeters read 0.3 ohm thru
the leads alone so all of the above resistances could be off.
Additional electrical trivia: Blaster 2 coil came with a 0.8 ohm rated
ballast resistor and Crane specs a 1.2 to 1.9 ohm resistor.
<snip>
Reason for this post is that my idle is rough/eratic and the car needs a
bit of choke (triple Weber 40DCOEs) until warmed up. Engine fires
IMMEDIATELY (when ballast resistor is bypassed) on cranking but if the
choke is not partially engaged, the engine will die with in a couple of
seconds. Crane's techs tell me that if the module input voltage is too
low the transistor does not know whether to fire or not - which could
cause a rough/erratic idle.
<
Aribert,
How do you have the XR700 connected? Is the red wire connected to the coil
+ terminal. If so try connecting it to a white wire somewhere that is the
full 12 volts.
Assuming the 0.3 ohm lead reading is an offset error (good assumption and
not a bad error for a less than professional grade DVM) then your ballast
resistor is 1.4 ohm and the coil reads 0.8 so the ballast resistor appears
to be kosher. The coil resistance is lower than the stock coil and it may
require the lower value ballast resistor. The problem is that this
combiniation may be too low for the XR700 which is intended for the stock
ignition setup. You may have to substitute in the 0.8 ohm ballast resistor
and a beefier ignition module.
Good luck
Dave
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